An astrophysicist is found dead in her car, and the investigation leads Castle and Beckett (Nathan Fillion, Stana Katic) to the possibility of an alien abduction. Meanwhile, a shady government agent (Lyle Lovett) tries to put an end to the pair's probe.

An investigation into a dockworker-turned-bar-owner's death leads Beckett and Castle (Stana Katic, Nathan Fillion) to the city's underground tunnels, where they discover a Prohibition-era secret. The probe's focus on New York's bar history inspires Castle to open one.

Beckett and Castle (Stana Katic, Nathan Fillion) tackle an upscale matchmaker's murder case, and they have company: the actress (Laura Prepon) cast as Nikki Heat, who wants a deeper grasp of her character. Her copycat image soon becomes too much for Beckett, but Castle likes it.

Castle (Nathan Fillion) and Beckett (Stana Katic) interview a top magician (Gilles Marini) after the owner of a magic store drowns in Houdini's legendary water torture tank. Elsewhere, romance is in the air for Esposito (Jon Huertas) and Lanie (Tamala Jones).

Beckett (Stana Katic) meets with the retired detective who handled her mom's homicide case, but he is killed right before he can tell her anything. The subsequent probe leads to a decades-old conspiracy that may reveal who murdered Beckett's mother.